What is the trough in destructive interference of EM?

Click For Summary

Discussion Overview

The discussion revolves around the concept of destructive interference in electromagnetic (EM) waves, specifically focusing on the nature of troughs and crests in relation to energy and photons. Participants explore the relationship between the electric/magnetic field vectors and the energy of EM waves, as well as the implications of these concepts in classical versus quantum physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the nature of the trough in EM waves, suggesting it implies the existence of "negative energy photons" that cancel out energy when meeting a crest.
  • Another participant clarifies that the crest represents the maximum magnitude of the electric/magnetic field vector, not the energy itself, and provides a mathematical expression for energy in EM waves.
  • Some participants express uncertainty about whether the crest can be equated to a photon, with one suggesting that the trough negates the photon temporarily when they meet.
  • A later reply warns against conflating classical and quantum physics, asserting that the crest and trough represent maximum and minimum field values, respectively, without implying the existence of photons at these points.
  • Another participant discusses the relationship between intensity and energy density, explaining that intensity is proportional to the magnitude squared of the electric field and outlining the process to derive energy from intensity.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of crests and troughs in relation to photons and energy. There is no consensus on whether the crest can be considered a photon or if the trough represents a negation of energy.

Contextual Notes

Participants acknowledge a lack of mathematical explanations and express uncertainty regarding the definitions and relationships between concepts in classical and quantum physics.

student34
Messages
639
Reaction score
21
My textbook says that the trough of the electromagnetic wave cancels out when it meets a crest. Okay, that makes sense, but if the crest is the actual photon/wave of energy, what is this trough that can cancel out the energy? It seems to mean that there are "negative energy photons" in between each "normal" photon.
 
Science news on Phys.org
The crest in the electric/magnetic field is the electric/magnetic field vector with the largest magnitude, it's not the energy. The energy in an electromagnetic wave is proportional to the quantity
$$
\int \int |\mathbf{E}(\mathbf{r}_\perp,t)|^2 d\mathbf{r}_\perp dt
$$.
where ##\mathbf{r}_\perp## are coordinates in the transverse plane.
 
Last edited:
  • Like
Likes   Reactions: student34
blue_leaf77 said:
The crest in the electric/magnetic field is the electric/magnetic field vector with the largest magnitude, it's not the energy. The energy in an electromagnetic wave is proportional to the quantity
$$
\int \int |\mathbf{E}(\mathbf{r}_\perp,t)|^2 d\mathbf{r}_\perp dt
$$.
where ##\mathbf{r}_\perp## are coordinates in the transverse plane.
I don't know the mathematical explanations of this, so I am wondering if you would you say that the crest is the photon? If so, the trough seems to being negating the photon for the moment that they meet. Is this right?
 
student34 said:
I don't know the mathematical explanations of this, so I am wondering if you would you say that the crest is the photon? If so, the trough seems to being negating the photon for the moment that they meet. Is this right?

No, the crest is not a photon. Be careful mixing classical and quantum physics like that. The crest is the maximum value of the E field in one direction and the trough is the maximum in the exact opposite (or minimum in the first). There is not a photon at the crest and an negative or anit- photon at the trough.
 
  • Like
Likes   Reactions: student34
student34 said:
I don't know the mathematical explanations of this, so I am wondering if you would you say that the crest is the photon? If so, the trough seems to being negating the photon for the moment that they meet. Is this right?
It follows from the definition of intensity as the energy density passing through a transverse plane per unit area per unit time. Intensity is proportional to the magnitude squared of electric field. If you want to get the energy, you then need to do the inverse operation as that to obtain the intensity, namely integrate intensity over the transverse area and then integrate with time.
 

Similar threads

Undergrad Energy of Electromagnetic Waves in Destructive Interference
  • · Replies 71 ·
3
Replies
71
Views
11K
High School What happens to the energy in destructive interference?
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Destructive Interference of two waves
  • · Replies 6 ·
Replies
6
Views
2K
Graduate What Do Peaks and Troughs in Light Waves Physically Represent?
  • · Replies 14 ·
Replies
14
Views
3K
Undergrad Constructive and destructive interference
  • · Replies 3 ·
Replies
3
Views
13K
Undergrad Interference and conservation of energy in a resonator
  • · Replies 28 ·
Replies
28
Views
3K
Undergrad Does destructive interference of an electromagnetic wave create negative energy?
  • · Replies 15 ·
Replies
15
Views
2K
Undergrad Mechanism of Energy Conservation in Zero-Amplitude Sum of EM Waveforms
  • · Replies 21 ·
Replies
21
Views
3K
Undergrad Crest and Trough Interference - Light Wave Explanation
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Can Two Laser Beams with Different Phases Interfere?
  • · Replies 10 ·
Replies
10
Views
3K